United Airlines passengers were facing major travel delays on Wednesday after the carrier suspended all U.S. flights due to computer problems.

In an emailed statement, United said it had a "network connectivity issue" and is working to resolve the situation. The airline didn't elaborate on the exact nature of the connectivity issue nor did it provide a timeline for when the problem would be fixed.

Separately, the Federal Aviation Administration said United flights were grounded because of "automation issues." The FAA didn't immediately reply to a request for more information on the problem.

The issue began Wednesday morning and knocked the airline's computer system offline, according to media reports and Twitter posts. Passengers were unable to check in for flights and United couldn't print boarding passes nor luggage tags. The glitch didn't affect the flight plans of United airplanes already in the air.

In June, United suffered a computer glitch that grounded all U.S. flights for around 30 minutes.

United is one of the world's largest airlines and flies to 235 U.S. destinations.